Coolant in fuel water separator

[Trucker rich]

Hello first of all I would like to say that I am new to this forum as a registered member but I've always looked at this site for insit and tips so thank you

Now for my question a day ago I get a message saying water in fuel and to drain water out, this alert would come on and off throughout my drive I parked it and drained my fuel water separator and it had about 5 oz of coolant .I am doing another trip to get money for this expense and I am draining fuel water separator every 120 to 160 miles with about 2 to 3 tablespoons of coolant coming out....my brother will be doing this job these coming days...so my questions are what should I be looking for to pin point more where the coolant may be coming from? Do you guys have tips to help with this job? Any answers would be a big help thank you

2016 kenworth t680 cummins isx 15 cm2350 927000 miles