At the risk of turning this into a bout out mutual backslapping (ahem), Rhythmstick has hit the nail on the head for me...
An evening of self-indulgence in front of a choice DVD (or three) can result in a handsome eruption, while a briefer (but admittedly just as satisyfing) sex session with a partner will produce a lesser volume.
But how can you catch *all* the drips in order to compare? ;-)