an interference fit therebetween to encourage a facile engagement the keys are rounded at their top surfaces 84 and bottom surfaces 86 thus top surfaces 84 and bottom surfaces 86 of the keys are disposed to respectively contact corrugated and smooth surfaces 66 and 68 of the keyways furthermore the figures illustrating the keys and keyways are paired to form pairings of fig1 a with fig1 a fig1 b with fig1 b and fig1 c with fig1 c to provide a proper sealing between cartridge 22 and housing 24 as shown in fig8 a 8 d and 12 an o ring 88 is positioned within an annular groove 90 in cartridge 22 adjacent its top wall 74 the sealing engagement provided by o ring 88 is enhanced as more clearly shown in fig1 by configuring the o ring with two pairs of upwardly and downwardly extending annular ridges 88 a and 88 b and an outwardly extending annular projection 88 c ridges 88 a and 88 b furnish larger areas of engagement with annular groove 90 insertion and withdrawal of the cartridge in and from the housing is facilitated by use of a tool 92 shown in fig3 and 13 15 the tool includes a shank 94 a handle 96 at one end and three arced t shaped projections 98 which extend from a surface 100 see fig1 15 at its opposed end the t shaped projections are provided with appendages 102 u2032 and 102 u2033 of unequal length with appendage 102 u2032 being shorter than appendage 102 u2033 fig1 depicts insertion.