This may get long, but I will try to share what I have learned being a turbo enthusiast over the past 7 years or so.
First off, I feel your pain I went through 3 different turbos with multiple rebuilds on each in under 2 years, and I jumped through my ass to get my car not to smoke. I was not successful even trying every option under the sun. Larger drain(or so I thought), different size restrictors, larger fitting on the pan, triple breathers for a fully vented case optimized clock of the housing and line routing, different oil weights and so on. It sucked big time mainly because some guys would have no issues or just change one thing and be good to go. Jumped on an oil-less turbo when they first came out in 2011 and have been running them ever since, love them. That being said I have since learned a great deal more about turbo design and why oil gets pushed past the seals.
Couple thoughts for ya first off, even if you may have corrected the issue there is often oil in the coldside and hotside still that can take a long time to clean out on its own, often need to pull it all part and clean it out manually to get it all out. Also I would do a leakdown/compression test on the motor to verify its healthy and your not pushing oil past the piston rings, once you rule that out. You can focus on getting the turbo issue corrected.
I also run a "FRPP/GT500" oil pump. The 3v and gt500 oil pumps are identical except the gt500 version has a higher pressure relief/bypass spring. So the gt500 pump will see a tad higher pressure than a 3v spring. They are interchangeable so if you still have the 3v one, may be a good idea to swap the spring. I found this out after the fact.
While pressure and flow do play a role in how quickly your drain cavity fills up, restricting the oil feed is a "band-aid" however with the oil pressure/volume the 3v has I feel it is necessary. I would go no smaller than .065 for a journal bearing turbo and no smaller than .035 for ball bearing turbo. Prior to the 3v the modular oil pumps had less volume and less pressure. These restrictor sizes will still allow for proper oiling of the bearings on the 3v so I personally would run them. 3an feed line is needed for ball bearing 4an feed line for journal. Journal runs hotter and needs more oil to lube and cool than ball bearing. Clocking. The accepted criteria for orientation for an oil feed turbo is within 20 degrees of straight up. However any angle will allow oil to get to the rings easier in the drain cavity. I would argue you want perfectly perpendicular to the ground and at most no more than 10 degree swing (5 in either direction).
However the consensus from manufactures and turbo companies that rebuild turbos and know their shit is that the real key to making it work is all in proper drain size and crankcase venting to prevent the drain line from backing up. The drain from the bearing cartridge inside the chra of the turbo is simply a gravity drain cavity and a drain hole designed to be large enough to evacuate the oil and not reach the rings, no feed pressure even makes it past the bearings so the "oil seals" see no pressure ( I did not know this at the time when I first got into turbos, I thought too much oil pressure is what caused oil to go past the rings and that they always saw pressure). There aren't actually "oil seals" anyway, this is a misnomer. The piston rings on the compressor and turbo side are designed to keep stuff out of the bearings/center section, not keep oil in. Hence why if oil fills up the drain cavity too quickly and backs up to the shaft and reaches the rings, oil will come right through them into the compressor or turbine housing. The coldside side ring keeps pressurized air out and the hotside ring (higher temperature rated) keeps exhaust and debris out on that side. I have learned that some employees at assorted turbo companies and many aftermarket turbo kit makers do not fully understand this either and don't put a lot of thought or design into draining the turbo properly they simple do what has been done or what they can get away with. I consider myself pretty knowledagable on turbo stuff and I'm still learning new things.
Drain lines for almost all kits for the 3v are abysmal and much smaller than the drain hole on the chra of the turbo itself. They often just come with a simple barb or AN adaptor that bolts to the bottom and right off the bat restricts the drain size. Your adaptor or and drain line NEEDS to match the size of the orifice on the chra period, to allow for proper draining under all conditions. You may get lucky with your setup not doing this. But it is the most crucial part. A 10an drain seems to work so a lot of guys see that as an upgrade, but 10an is too small! Almost all turbo chra's across many makes have a 3/4" orifice or larger. So you need a drain fitting and line that is at least 12an or .75" inner diameter. These standard oil drain adaptors that come in kits and that you find all over online are mostly garbage for what you really need. From there make sure you have a nice sweeping arc on the line to the pan, no part of the line should go lower than fitting on the pan. Also avoid bends with fittings as much as possible, if you can do straight fittings on the chra outlet and into the pan that is idea. If you have to have bends to fit your setup try to keep them at 45's vice 90s etc. Next is the pan fitting, DO NOT shrink this down either, you want to keep that same inner diameter there that you have at the chra and line. 3/8npt's inner diameter is to small. You want at least a 1/2npt fitting at the pan which has a an id of around .78" at the narrowest point of the taper.
Last part of the puzzle is crankcase pressure. Which your setup and motor health plays a role in this. Under boost there is pressure in the compressor cover and turbine, which will help reduce any backed up oil coming past the turbo rings which is a plus, since piston ring blowby is higher and the drain does run slower under these conditions. However if you have excessive blow by on the motor and aren't venting crankcase pressure properly you will get oil backed up under these conditions. An open system with breathers or a vented catch can seems to work best for a turbo. So breathers on the valve cover or lines to breather catch cans is idea. If you can make the barb and line sizes bigger go for it. I also highly recommend a oil filter cap breather, its a much larger hole to vent out of.
I tried doing these adjustments in stages as I learned while getting the turbo checked out, rebuilt or going to a new one and personally never resolved the issue,( I only had a 10an drain and had some bend fittings as I thought it was adequate). If you want to learn from my mistakes my recommendation would be to do all of this stuff at once, with a huge emphasize on the drain line size. And start with a new turbo or one that has been checked out and is good to go. And ensure all the piping is cleaned out.
Good luck!
