If you are very, very lucky, the stars will align at this moment and when you nip to the toilet before dashing to Lidl, you will discover that toilet user or users unknown have once again left skid marks and pretended not to notice.
Decide that your strategy must change as neither cleaning it up without comment nor cornering spawn one at a time and sensitively broaching the subject to be met with shocked expressions and claims of 'That definitely wasn't me' are clearly not long term solutions.
Instead, gain the attention of all present and temporarily remove screen privileges. Distract with dinner-related tasks and explain what is about to happen. Prepare for resistance, but power through and point out that the pizza will be ready in 7 short minutes, by which time the unpleasantness will be over.
Assemble in the bathroom. Explain to the spawn that they can determine the order they clean in, but that everyone will get a turn. In fact, everyone will get more than one turn if that's what the job demands. Hand out the toilet roll and bleach and supervise the queue.
Be surprised at how efficiently the job can be done. Supervise the squirting of the bleach and the final flush. Congratulate your team as they wash their hands and file out the bathroom.
Job done. Not only is the toilet bowl perfectly clean and ocean fresh, but tensions between the spawn will have melted away. They will have bonded with each other during this team building exercise and now be united in their annoyance with you. Luckily you are an adult and your sense of self worth does not depend on their approval.
Eat pizza together 7 minutes later and discuss the best bits and worst bits of your day. The worst bit will be likened to class detentions which apparently 'never work'. I disagree. The object lesson was clearly effective because we're still talking about it and the toilet is clean.