Why does the toilet spontaneously combust????

Ok, good to know. whenever I looked up answers for toilet catching fire the only thing that came up was seeing the little flame in the toilet, nothing about how to fix the spontaneous combustion 

Also, something to remember:  If you've earned Handy by completing the Nerd Brain aspiration, "Instant Upgrade" will do that upgrade, so you might not want to Instant Upgrade toilets.  And I don't remember if you said you use mods, but if you do:  Upgradios, a custom spell made by LittleMsSam, has been made to purposely leave that upgrade out.  It's supposed to be either composting container or water recycler, her spell chooses water recycler.  If you wanted composting container, you can upgrade that first like some common Muggle, then Upgradios the rest afterwards.

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? latest
What expansions, game packs, and stuff packs do you have installed? a lot
Steps: How can we find the bug ourselves? upgrade toilet with a compost container, it says if it is not emptied it will catch fire. it happens all the time when it gets full. there is no way of avoiding this. it has straight up killed one of my sims recently. i feel like there should be a way to avoid this but no option to empty anything shows up. this has happened since ive downloaded sims 4. im pretty sure its just a base game issue.
What happens when the bug occurs? upgrade toilet with a compost container, it says if it is not emptied it will catch fire. it happens all the time when it gets full. there is no way of avoiding this. it has straight up killed one of my sims recently. i feel like there should be a way to avoid this but no option to empty anything shows up. this has happened since ive downloaded sims 4. im pretty sure its just a base game issue.
What do you expect to see? there should be an option to empty the compost bin when it is full so you know before a sim uses it to empty it or they could die via the impending fire.
Have you installed any customization with the game, e.g. Custom Content or Mods? Never used.
Did this issue appear after a specific patch or change you made to your system? No

‌

upgrade toilet with a compost container, it says if it is not emptied it will catch fire. it happens all the time when it gets full. there is no way of avoiding this. it has straight up killed one of my sims recently. i feel like there should be a way to avoid this but no option to empty anything shows up. this has happened since ive downloaded sims 4. im pretty sure its just a base game issue.

@crazyleah17 There's a very easy way to avoid the problem. Buy a new toilet. You can put the composting toilet into storage until you have a bug farm, or just sell it. I know that seems like a nuisance, especially if you added other upgrades, but it's still the easiest thing to do.

Thank you so much, this has been bugging the hell out of me.  My main sim has been autonomously upgrading things, including toilets, so I didn't even realize it was done, that's really annoying, but at least I understand why it's happening now