Chesca has said it all there really
Plastic tubes connected to cages aren't that great for hammies really as they do tend to do this - block them up and nest in them. It's their instinct to block off any tubes to stop predators getting in
They do better with tubes or tunnels as floor toys. A simple kitchen roll inner tube is popular and can also be chewed, which is good for their teeth and fun for them.
Is the Ferplast mini duna? Do you have stoppers to block off the tubes? If so I would remove them and block them off. Your hammy will then rebuild his nest elsewhere - maybe in the house. A house that is open underneath and on top of the substrate is best as they like to bury hoards under the nest.
I believe dwarf hamsters are a bit more difficult to toilet train than Syrians. As Chesca says if you give him a sand bath he will probably use that to both roll in (it helps clean their fur) and as a toilet as well. Then you can just scoop out the wet bit and leave most of the sand. You need to use Chinchilla bathing sand though, not just any old sand, and not "dust". It's sterilised and suitable for Hamsters.
An old ice cream plastic tube or any pyrex dish eg would do as a sand bath. The tubs of sand last quite a while.
The other thing they need to have normal behaviours is plenty of deep substrate - at least 3 to 4 inches but as much as you can fit it. It makes them happy - they can dig and burrow in it and if it's deep enough they can even dig their own tunnels and burrows. If you're using pine shavings (assume that's what you mean rather than actual sawdust) then check that they are kiln dried and dust extracted.
Poops - don't worry about those
They aren't dirty or smelly - they are like little hard seeds and hamsters sometimes hoard them and/or eat them. They have two stomachs and can redigest extra vitamins from their poops - it's an instinct in case there is a food shortage! So every time you take the hoard away during a clean out your hammy will probably hoard more poops in case there's a famine lol.
Anyway rule of thumb is - deep substrate and spot clean, rather than a big clean out. Spot cleaning is just removing the odd handful of pee'd in substrate and replacing it with a new handful, then mix it in a bit so it smells familiar. They scent mark to find their way around as their eyesight isn't great, so removing all their familiar smells in one go is stressful. You can mainly spot clean and then do a bigger clean less often which helps their stress levels. Plus if your hammy starts using the sand bath as a toilet it will help, and when the substrate is deep the bottom of the cage often stays dry anyway.
Cleaning - there's no need to use pet disinfectant. Just a warm damp cloth will do or warm soapy water (eg washing up liquid soapy water) then rinse and dry. They only need disinfectant if there is illness or disease. Scents can cause problems for them in terms of breathing and stress as their sense of smell is much more powerful than ours.
I would try and get him settled a bit in the current plastic cage with the tubes removed and then look at upgrading it to something bigger. Something like the Ferplast Duna Multy is a good upgrade (no tubes with that one). Not too big, not too small.
Cage Duna Multy
When you upgrade you could just put the whole cage base inside the newly set up new cage and let the hammy explore out from there, so it still feels and smells familiar.
Enrichment is the keyword for a happy hamster with normal behaviours. That means lots of variety in the cage, levels, textures, things to do and places to go - so lots of substrate, a good house big enough to build a nest in, a suitable sized wheel that works properly, food and water obviously, a sand bath and plenty of hidey places and floor tunnels/toys to climb over, run through, plus some kind of shelf or level is good so they don't feel too exposed from above and can sit under it or climb on top of it. For a tank style like the duna multy you can just make one out of a piece of wood with four dowels stuck on for legs (kiln dried untreated pine is fine).
If you get a new cage all set up and ready before moving the hamster in it helps as it's best not to make any changes for the first two weeks when they settle into a cage. And no cleaning for the first two weeks except a little bit of spot cleaning.
Your hammy is probably trying to avoid his nest and hoard being taken away so he's blocked himself into the tubes.
They generally are very clean little things - they groom regularly. I think when they are young they do tend to just pee in all sorts of places at first until they get into a bit of a routine and often pee in the wheel, but just giving it a wipe now and then will do and only a full wash every month or so.
When doing a big clean, even then it's best to only replace half the substrate and replace the dry half and mix it in with the new. Plus clean toys at a different time to the substrate - eg a week or two later - and the wheel at a different time again. So something always smells familiar.
Also if they are cleaned out all in one go, too often, they will start peeing on everything to scent mark it again so it can become an itch scratch situation!
This is the Chinchilla bathing sand
https://www.amazon.co.uk/Supreme-Pet...a+bathing+sand