Honestly buying uniseals was the most expensive part in my system too. I had them left over otherwise I would have gone with proper bulkheads that have a screw connection. 3" is good, bigger is always better but that was the largest I went due to cost. The input into the system can be smaller though as it has the pump forcing it through.Forgive me if you've answered this, what are you using for your bulkheads on the sites? Also, what was your solution for the return to epicenter outside the tent? How'd you go about light sealing and ensuring the fabric didn't tear over time?
I'm looking at building a much smaller UC system and the biggest hurdle I've come across is the bulkhead choice. Plus, cutting a hole in the tent, but that's nothing compared to pretty much the only 3" bulkheads I've found are made by CC, and at $20 USD a piece, for the amount I need that's $180 just by itself.