During the first two minutes of the 10-minute pouring period, teams are allowed to tamper with their waste water as long as the tampering keeps the water within the 2 five-gallon buckets and does not reduce the amount of waste water to less than the original eight gallons. Therefore, the only transfer of waste water must be from the two buckets directly to the team's water filter. Any materials used must be on the Approved Materials List or part of a team's approved three "unique" items.
The details about this two minute "free interaction" period are explained on page 5 of the Water Treatment Rules, number seven of section "G. Treatment Phase." Teams will be penalized 10 points for every minute (rounded up to the next minute) after the beginning two minutes that a team interacts with their waste water and/or treatment system directly, besides preventing "catastrophic events."