Severn Trent Water, which operates many wastewater treatment plants in the Midlands, has started banning tankered elsan waste which contains formaldehyde. Other water companies are likely to follow. Boats with a pump out should have no need to add chemicals to their tank (unless it is a drop through). But the majority of boats, as well as caravans and camper vans, rely on portable toilets that which use a chemical to mask the smell of the waste the most popular containing formaldehyde which kills the bacteria water companies rely on to treat sewage. Many chandleries now sell formaldehyde-free loo treatments. Other ideas include sodium percarbonate/washing soda but be careful about using other cleaning materials at the same time to avoid producing hazardous gases from the reaction.

Water companies refuse to allow elsan waste to go into the sewer system to limit formaldehyde reaching their treatment stations. Tipping your porta potti waste down the flushing toilet is not the answer (and never is because of the mess it makes).