What’s the best type to buy & how long do they last? Before now, I never realized there was a gasket in there. Need to replace. Should I buy a few just to have on hand?
I've always used the nylon gaskets but the fiber ones should work fine as well.
While many fill stations provide one with a fill, you still want to keep a few on hand...
It depends. If it's Taprite brand, they use a specific square profile "oring". If that's not the case, any nylon or fiber washer is fine but they are both generally considered a one time use to be replaced with each tank change. I've made a perfectly functioning gasket for this junction by cutting a donut shape from any LDPE container out of the recycling can such as: