Is it normal to talk to my teenage sons about getting semen on their sheets?

This question may seem odd, please read and help. Thanks!

I'm a proud dad of five boys who are at "that" age. My oldest son is 16, twins boys are 15, 14 and the youngest is 12. As a dad, I understand that they're growing up and that at their age they're developing and starting to masturbate all the time and get wet-dreams. I've even caught some of my sons jerking off in their room by accident, so I know it's happening. I know it's normal for teenage boys to masturbate all the time, so whenever my boys close their bedroom doors or take a long time in the bathroom, I just let them have their privacy.

But there's got to be some way I could control the amount of semen on the sheets every week. I'm a single father and I do the laundry (I've assigned chores to all my sons, and laundry goes to me). I take the sheets off their beds, and it would be covered in semen. I wash their boxers and I can see patches of semen that they thought would just dry up and I wouldn't notice. At first, I was glad to know my boys are functioning just fine because I noticed semen on each of my son's beds and clothes. But I didn't expect to have to deal with a lot of it.

A friend gave me advice and said to put tissues next to their bed. So far my 16 and 15 year old sons use the tissues (I've taken out the trash from their room it's filled with tissues. Then I realized they used it to clean themselves up after jacking off, and I don't get weird about it. I'm just glad less of it gets on the sheets). Even after doing this, I still find the stuff on the sheets and some of their boxers.

And I know the solution is to talk to them, but how do I open the discussion. I'd make them do the laundry, but they all have their own chores to do already and laundry's mine.
I've given them the sex talk, but this is a tricky one. How should I deal with this?