You're just asking to be scammed here. You'll get plenty of posts here and plenty of PM's about surefire RWT methods.
While there are ways to transfer large sums of money from one account to another, none are completely safe from being detected by Jagex.
READ MY LIPS: There is no completely safe way of transferring gold/items that Jagex will never detect.
You might get away with it, and you might not. If Jagex catches you, you'll get banned. I don't know of many who won appeals for RWT.
Before all the rest of you go saying that old middle-aged Brogan Sue doesn't know what she's talking about, let me tell you what happened to my friend's son. He was transferring some gold from his main to his pure. All he wanted to do was transfer about 100,000. He did it the supposedly acceptable way of Party Room on slow servers late at night. He was successful in transferring three Rune Plates, and when he was done, he went to bed.
When he woke up, the main couldn't log in. Appeals were denied. He was screwed.
That's correct: He got a level 93 account with about 80 million worth of gold and items on it banned permanently for breaking Rule 12.....because he transferred about 120k in three Party Room sessions.
People on the Runescape forums have complained about being banned for using BH, for using Party Room, for using newts and other low-shop/high-GE items, etc. The bottom line is that if the same two accounts keep transferring over and over, there's a good chance that they'll get caught and be toast. It's possible that they'll get away with it, but it's also possible that they won't.
I know that some will come forward and say: I've done this for three months and never got caught. My answer is: You were lucky (or not unlucky), and it's getting tougher, because Jagex is working on detection algort
Good old Jagex is watching, so be careful out there. Nothing is 100% safe.