I don't understand the problem here.
A paid consultant has spent their time with you. seen a risk you hadn't, and advised you to create a simple document.
This is how I imagine the conversation and ensuing actions went :
Consultant: "Golly, those drains from the sewer are directly beneath right where y'all put all of your food contact product that's ready to ship. Maybe you should have a map of the drains so that if the sewer backs up you'll know which warehouse locations to check for damage"
Or "Gee, it looks like you haven't cleaned those drains in a while. You should add them to your cleaning schedule and make a map so you know which one to clean"
or "Wowza! You have some drains you never clean because they are dry. You might want to designate those on a map so an auditor doesn't expect you to clean them"
You - <Grabs emergency exit map off wall> <copies it> <draws three dots on it> <crosses out "Emergency Exit Map"> <Writes in "Drain Map">
How did that series of events not happen? Why are you paying this consultant if you don't trust their expertise? I can see questioning the need of a significant process change or unnecessarily elaborate program, but drain map? Just make one, dude. You could have done it in the time it took you to post & read the responses. Work with your consultant - they are there to help you.
As mentioned, ti's good for sanitation purposes (cleaning schedules etc) & environmental monitoring identification - and if you ever discharge large volumes of water, the city water guys might want to come check them out.