DNA purification after agarase treatment

[C Coward]

Greetings,

We're considering using beta-agarase to prepare HMW DNA from a pulse-field
gel slice. We're wondering about the best method to purify the DNA after
agarase treatment (the downstream application is a transposition reaction
which we need pretty pure DNA for). Suggestions so far are

-drop dialysis (any suggestions of membrane pore size?)
-isopropanol precipitation, which apparently shouldn't precipitate the
agarase digestion products (anyone with any experience of this?)

any other suggestions?

TIA

Chris