Nick you will need to check with your local epa about cleaning the dock, We have three that one person owns we tol them that we would not do the job since the waste water can't come in contact with a body of water. I then called my local epa they told me that we can clean the dock but gave us the ONLY WAY TO WASH IT was NO CHEMICALS and we had to use the lake water to wash with to prevent the tap water with chlorine in to to enter the body of water.
By the time that we used lake water and sent it through filters to clean with with out the use of any chemicals we passed on the jobs, its better to pass on them instead of getting fined.