trg3dp published a SCAD file to create custom caps for beer growlers and gallon size jugs. I printed one of trg3dp's caps and found it could not seal fluids into the jug. I stated with trg3dp's scad file and provided further customization. You may now enter a different height and inside and outside diameters.

My SCAD file modifications additionally produces a seal insert to put inside the cap. If you wish a fluid seal on the cap print the insert in FLEX and pop it into the PLA printed cap.

Once you have you STL file, click split into objects. You will get the cap separated from the seal. Hide the seal and slice the cap for PLA. Then hide the cap and enable the seal and slice in FLEX.