I've done what John recommends in the past -- and it's the way I "store" my 1924 tuba between it's more or less semi-annual uses. And I did it to my Cerveny BBb rotary tuba for a period of years. However, for my Eb Wessex tuba -- which I haven't played in about a year and a half now, I went an extra step -- primarily because I KNEW that those tight piston valves would stick if I just left them sit for that long, lubed or not.
In that case, I did everything that John recommends, and then cut four sections of PVC pipe, got end caps for them, and put the cleaned and dried pistons (fully assembled) into those for storage. That way I KNOW that when I go to get the horn out and play it I won't have stuck pistons I'll need to deal with -- and the pistons are fully protected so that nothing can accidentally affect them.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)