You spawn at the stone pit and you need to build Satsuma. You have the moped at the stone pit so you can go to shopping and find the septic truck. Satsuma is already inspected so you don't need to.
You can find the engine from garage (home) and you need to build it too.
You need to find the septic truck from Peräjärvi village it can be anywhere! (if you don't find it hit me up in steam.)
You need to tow Satsuma to garage (home) and install the engine when you have built it.