The act of urinating, usually over oneself or over someone and / or something.
One can swamp oneself in public or private; clothed or unclothed. Swamping oneself when wearing stone-washed 501 jeans results in the much admired 'Map of Africa' pattern. Women find this look very attractive.
One can swamp over someone / something else usually when staying in an unfamiliar place, therefore causing oneself to become disorientated and unable to navigate to the khazi. This isn't always the case, however, as there are numerous reports of squaddies swamping on sofas and their own beds (single, double and multiple occupancy of which does not put off said swampee). Moreover, squaddies have been known to swamp over other squaddies (wives / girlfriends / pets / siblings / parents); into wardrobes / lockers; into boots & shoes; into Bergans. A swamping squaddie can be likened to the Martini Girl: Any time; Anyplace; Anywhere.
The squaddie habit of swamping the bed has resulted in the issuing of plastic coated mattresses. These mattresses are also to be found in old people's homes and mental institutions, which coincidentally are places where MDN can often be found loitering with intent.
The military has a curiously ambivalent attitude to swamping. Anyone who admits to it on their recruiting forms is unlikely to be allowed to join the Army, but those who conceal this exciting character trait achieve a semi-heroic status once safely in and can indulge it to their hearts content, though they are rarely offered the top bunk in transit accomodation.
It's worth mentioning that in these politically correct times, when we aren't really allowed to be judgemental, the question about bed-wetting on the army recruiting forms is a kind of disguised IQ test. Anyone applying for any job who answers 'yes' to the question 'Do you wet your bed?' is clearly lacking the intellectual acuity for any military trade (except, possibly, the MPGS when numbers are down). Swamping itself isn't necessarily the sign of a complete idiot; admitting it on a job application undeniably is.