Are you SURE they need to be replaced? Did they crack? If not, it may be a simple matter. 34 bulkheads, not counting the 5 in the sump, or teh six in the water storage array (going through round Rubbermaid cans). None of them leak. One was shipped cracked, and one had a weird inner diameter that fit nothing. If you can drain (and you'll need to to install new ones anyway), simply dry the area outside, loosen the flange as far as it will go, and put a healthy bead of silicone completely around the flange. Tighten it up and use the silicone that squeezes out the side to seal the back edge that's up against the threads. If all of your bullkheads started leaking, they were either installed wrong (usually washer on the wrong side or backwards), or possibly tightened too much (hope it didn't crack the tank), or too little. Hand tight is a little too loose for me sometimes and I crank it a tiny bit more with a wrench.
