Leak In Black Water Holding Tank

[Jake]

Have a 2004 25' Safari. Did the morning walkaround and noticed a pinhole size leak in the black water tank. This would be on the tank cover. I am assuming that the black plastic "boxes" under the trailer are in fact coverings for the actual holding tanks.
Quite cold last night here in West Memphis so it may be condensation but will do the "odour check" later.
Any suggestions on repairs.
Forums have always come thru.
thnx
jake