An antiquated form of cheating used in the 70s by competative swimmers and track runners.
An athelete has some of their blood removed prior to a match (far enough in advance that the body regenerates the lost blood) and then immediately before the competition redeposits the extracted blood in their body. This process gives the athelete highly oxidated blood which enhances their performance.
It is no longer done as nowadays advanced performance-enhancing drugs can replicate the effect.
When two people go "tag-team dumping" it is similar to tag team wrestling except that after one person has dumped they leave the toilet without flushing and the second team member goes in and dumps on the existing dump. In a competition format the first team to block the toilet wins.
Belly Boy & Big Kev make a great tag team dumping team - the amount of orange juice those guys drink in the morning means they can dump for Britain.
Heard the noise when the big bald guy from the office next door is taking a dump - he'd be a great tag team dumping partner!