how old? it doesnt appear to be too runny, as long as the poo itself is solid i believe you should be good... is there any foul smell to it? besides the obvious of course...
mine use to only use a small food bowl for his duties, and then he changed it up and started to use different areas. If you can get him to use a single area that'll make cleaning up a breeze for you... Our Fred only poos outside in the grass so every other day he gets some toilet time and some exploration.
The squash has a lot of water so that could be it.
You need to check his fat pads not his ribs for weight loss. Also you can get a little kitchen scale and track their weight. It helps if anything is up health wise as they don't always show problems until it's too late.
One of mine was getting skinnier but putting on weight. This was due to an abdominal tumor . So it can be a useful tool in keeping your little buddy healthy.