An inexpensive bottle cap for either GL-45 or GPI-38 threads that permits standard solvent or media bottles to be used as an HPLC reservoir. Caps have two holes to accomodate 1/8" tubing and one hole that accepts a standard luer inner joint. Caps are made from polypropylene and the inserts are made from Tefzel. Complete cap assemblies consists of the cap, tefzel insert, (2) plugs for the 1/8" tubing openings and a plug for the opening.