| Is the leak around the outside threads between the bulkhead and tank? Are the nuts on the bulkheads on the inside where they can be removed or on the outside where the pipes go in? Usually leaks are from areas of distortion between the places where surfaces fit snugly. It's not the tightness but the distortion. Sealants are really there to take up the spaces between the snug fit areas.
Silicone sealants aren't actually very good in comparison to eurethanes. Silicones great advantage lies in "extrememe" heat and cold resistance which ponds don't have and silicone sealants don't really stick to surfaces well. The polyurethane sealants that we use are usually moisture cure, adhere better and are stronger structurally. If the leaking is between the bulkheads and tank wall you could back off the nuts, remove the old gaskets, clean everything with 91% rubbing alcohol and apply polyurethane around the threads between fitting and tank and snug them back up. Wipe off all visible excess with 91% rubbing alcohol so nothing is visible. Visible "ooze" is always a source future problems because it is attached to the sealant below it. Over time that "ooze" will loosten or be pulled at and cause the sealant below it to be removed.
Many times fittings start to leak after a period of time because of alkalinity leaching which slowly forms tracks to the outside and expands over time eventually causing a leak as opposed to the almost invisible "sweating" that started it. Expansion and contraction can also create pathways of sweating that can start this.
Unlike other sealants, polyurethanes are nasty to work with. Use lots of latex gloves and throw them away often and in a secure place. |