Bulkheads are fine if you are working with plastic tanks. If you are simply connecting piping through the liner, I would suggest a pipe boot. You cut a hole in the liner half the size of the pipe, shove the pipe through. Then cut a washer out of rubber, same diameter as the pipe, with a hole in the middle. Put this over the liner to protect it. Then put a Marine Grade Stainless Steel clamp over this and tighten. The liner is at a 90 degree angle to the connection point, and its a continuious clamp so I would say it is way stronger than a bulkhead fitting. Have you ever tried to pull liner away from a bulkhead fitting, its pretty easy.
With commercially made bottom drains, you have the main hole, and then you also have at least 8 bolt holes, which is more opportunity for leakage. Not to mention thats not a continous clamp, but tight and weak spots.
Pipe boot can go through the liner at the bottom or the side. This is no problem. I often leave a slight wrinkle in the liner below vertical boots incase the ground were to settle and strech the liner. Liner has 200% elasticity.
Here's how many pipe boots I have on my new koihouse pond:
- (6) 6" boots through the side (about 30" down) connecting settling chamber to pump chamber and pump chamber back to pond. One boot on each side of the pipe.
- (4) 4" boots through the bottom (5' depth) of the main pond connecting the bottom drains.
- (4) 4" boots (2 in each settling chamber) through the bottom of the settling chamber. This is where the water enters the settling chamber from the bottom drains.
- (4) 4" boots through the side (about 12" down) connecting the skimmer pipes from the main pool to the settling chambers.
- (3) 3" boots through the bottom of each filter chamber for waste drains.
- (1) 2" boot through the pump chamber as an overflow.
So that is 24 pipe boots total at under $2 each. Imagine if you had to do that with bulkhead fittings or commercial drains. Whats a 6" bulkhead fitting cost? Whats a commercial drain cost?
You can pipe boot anything round... Ive done 55 gallon barrells for example to use as header pools for filters.