We sort of wing it, whoever is closest to the guy who gets drained. If there's nobody close there's something else wrong entirely, and in that case we had some random melee take it or whoever was first to say "i'll get it". I haven't done Durumu10m normal in awhile, last time I did was 3 weeks ago or something and I was healing. We 2man heal and 2 man tanked it, possibly 1man tanked, I'm not sure. I don't think we ever have more than 3 people take a single beam.
It helps if everyone is sortof vocal and initiatives are being taken. Contrary to 25man, which may be your issue, 10man is a lot more about what individual players do and decide to do and there's a lot less pre-planning possible, and less handholding (25man: "g1 takes beam, g2 3 4 5 ignore mechanics and nuke") too. If your players are incapable of daring to take decisions on a fly when they are needed, without being ordered to by RL, certain mechanics that require quick thinking and reaction, like life drain, may become a bit more complicated.
Encourage your raiders to step up and speak up and do what is necessary, at the risk of making a wrong call every now and then. That's what will make a 10man raid succesful in the end, and it's also the most common issue a lot of 10man guilds struggle with: no initiative, too passive playing.