Transact SQL :: Reading Text From BLOB / Varbinary Objects

We have an interface where we receive data from an external supplier. One of the fields in the interface is of type BLOB (the source is an Oracle database), which would be read into our MSSQL database as image. This can also be converted to varbinary, and a typical field value looks something like:

0x70697A5F8F000000789C0DCCBD0DC2301....etc. etc.

However, we know that the origin only contains text, and we even know the text from the GUI they supply us with. The text could typically be "Delayed by 3 minutes because of water damage" or something like that.

What I want to do, is to extract that text from the field.

First, I have stored the incoming data stream in a table, where one column is of type varbinary(max). It looks like this goes swell. But I don't know which command to use in order to get the text extracted.

I have tried these:

1) select master.dbo.fn_varbintohexstr(Myfield) from Mytable
-> Returns just the text "0x70697A5F8...." which I have no interest in

2) select cast(Myfield as varchar(max)) from Mytable
-> Returns just Chinese signs.

3) select cast(Myfield as nvarchar(max)) from Mytable
-> Returns just Chinese signs.

4) declare @ptrval varbinary(16)
select @ptrval = TEXTPTR(MyField) from MyTable   -- with MyField defined as image
READTEXT MyTable.MyField @ptrval 1 30
-> Returns just the text "0x697A5F8...." which I have no interest in

Of course, since only text is stored in this field, the field should never have been defined as BLOB in the first place. But the source system is external, and it's a standard system, so we may not alter it in any way.