Can't open deckfill.

[Dick Kobayashi]

Many good recs here. I know this problem. Addressed successfully with pb blaster for a few days and gently but continuously tap to unscrew with a cold chisel and hammer. Once the cap broken free I had no trouble removing. How to prevent? Dunno. But I found it was not necessary to tighten the cap much to keep the sewer gas in the tank and venting through its proper vent. That and leaving it only partially screwed in during winter was helpful. Sewerage and associated gases do not need to be hermetically sealed off. They aren,t going any where bad if the tank vent is not clogged. Good luck on this, Dean.