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Hello Canalworld! Firstly, thank you so much for the wealth of knowledge and advice that I've received from you all over the past couple years, and all without ever having had to make a post. I knew the day would come though. I've owned my 55ft narrowboat built in 1991 for two years now. She was built by R&D, and had a survey on the hull in 2019. The thinnest part of the baseplate that came up with the ultrasound was 8.8mm on what was originally 10mm steel. Myself and my wife have been living on board full time for almost two years now. There's always something to do in terms of maintenance, and I've kept on top of it so far. We love the practical hand on approach to life. Recently, I'd noticed some white mold had been growing on some of the plywood that makes up the under-bed storage, where it is sat near to the black water toilet waste tank. This is a large (I have no idea of the capacity) grey plastic tank that sits under the bed, cut into the wooden floor and extending below the wall and into the bathroom, with a drop through toilet installed. Upon further inspection, I discovered that the ply of the floor had become weak and brittle around the tank, as if it had been exposed to lots of damp and then having dried over the summer. After having ripped some of this weakened wood away, I've discovered just how rusty the floor has become underneath. Large flakes of on average 6mm thick rust can be easily pulled away from the floor all around the tank. I'm aware of this apparently only being 0.6mm of steel lost, or a tenth of the thickness of the rust. How accurate is this however? And would this have been counted as good steel during the ultrasonic survey, or are they pretty accurate in just measuring the solid steel? It appears that there is a thin rubbery coating on top of the rust. I guess this is old treatment/coating that seems to have done more harm than good. The moisture appears to have gotten underneath and even been trapped by it, which has caused the rust to bubble up with the coating still on top. This looked quite dramatic and worrying when it was first revealed. My suspicion is that the black water tank is causing condensation in the winter. The tank is not insulated, and only had a single sheet of thin polystyrene placed, not secured, on top of it. This had began to smell, I assume from the damp and mold, and has now been removed. I am (mentally) prepared to scrape back and treat the area with Vactan, having done a similar job on the rusty welldeck. However, I'm of course worried about putting a hole in the floor. I've heard it from both sides: "It's always at least 10x worse than it looks, so get in there with the scraper and grinder" Vs "I put my finger straight through the floor of my boat and tickled a fish" Essentially, I'm looking to insulate the black water tank, so as to stop further condensation. What would be the best way of doing this? I assume that I'm going to have to move the tank anyway to get to the rust below and treat that. Afterwards, should I wrap it in something? Try to coat the entire thing in spray foam? What about the bottom? Fill the gap between the floor and the tank with foam? I have a big pot of Vactan, but what else should I put down on top of that, if anything? And ultimately, would I be wise to wait until I can have her pulled out of the water and then scrape back all the rust, or will I be safe to go for it whilst she's still floating? I've been hoping to apply fresh blacking early next summer, but I don't want to have to wait until then to fix the problem, especially going through another winter of condensation building up. I also don't want to leave it to get worse for any longer than I have too, but I'm also not made or money (otherwise I'd be in dry dock already). And in the worst case, any recommended dry docks between Tring and Northampton? I shall attempt to upload some small videos that I have of the problem and be back to update. Here's a screenshot showing underneath the tank. The grey at the top left is the tank, which is sat on the steel girder that runs across the floor (do these have a name?). You can seen the moisture on there. This photo does not show the full extent of the rust. Thank you for reading my life story. Edit: I've uploaded three short videos showing what it looks like under the floor and the tank. https://streamable.com/82wcmo https://streamable.com/5lx2dx https://streamable.com/lz5kip

Hello, Looking for some advice regarding our waste tank situation. The boat has a pump out toilet with large 1000l waste tank. It is quite smelly inside the boat and we’re trying to narrow down why this is. The tank is identical to the potable water tank on board. Could this be the issue? Not the correct tank? Link to the tank below: https://www.directwatertanks.co.uk/1000-litre-new-schutz-ibc-steel-pallet-un-approved?language=en&currency=GBP&gclid=CjwKCAjwoMPcBRAWEiwAiAqZh94zhssTN0p7KAMB2Jkx4PVkj8vG62Nk0lcVzs92kPXjVSiFedCZZRoC3ysQAvD_BwE If not we’ll have to investigate other possibilities. I’m thinking pipework, seals, tank lid, tank treatment- we use Elsan blue as this had been used previously so more organic options weren’t available to us. Anyone got any ideas of most likely scenario? Many thanks, Jo

I have scoured the forum the best I can, and found a few answers that have informed me, but think I need to ask a fresh question... I have just removed an old plastic pump-out tank - disgusting work but all OK. However, after shifting this tank I discovered that the boat has an older metal waste tank under the floor; possibly built into the hull but I am not 100% sure. The older tank wasn't sealed, with just a piece of wood over the old 'drop-through' hole. I was surprised to find it nearly full to the top with (orange) water. I thought this was old sewage, but having stirred a stick around it doesn't bring up any sludge so am wondering if a previous owner had flushed it out and just left it full of water, which has since mixed with rust. My question is: I want to pump out this old water, but am unsure whether to A) try to dry it out and leave it empty or keep it filled with water which I have read in some places will stop the bottom rusting. My gut goes with option A, but I wondered if it would still rust? Any suggestions on what to do to deal with this old tank (without removing it) and sealing it back up would be much appreciated! (If it helps, the boat is an ex-hire Canaltime / South West Durham build from 2000.) Thanks in advance!