I created and tested with my tank a replacement rubber seal. I printed it with soft TPE filament and the result is great – smooth turning without leaks. The model itself is rather simple: height 5.0 mm, outer diameter 20.0 mm, and inner diameter 11.3 mm.

Recommendations for printing are as follows:

• the main secret is filament – it should be really soft. I tried several, and Recreus FilaFlex82A worked the best. I suggest downloading the following printing profile for that filament
• layer thickness: 0.2 mm
• infill: 5-10%, Gyroid
• two top and two bottom layers
• speed: 90% or slower
• no supports
• TPE has enormous adhesion, make a test print if you try it for the first time. Reduce adhesion with a glue stick, if needed.